Due to demand for decreasing CO2 emission and improving fuel-efficiency of vehicles, there is a rapid development of electric vehicles (EVs). In general, an EV includes at least one on-board battery for driving an electrical motor and for supplying electric power to electronic devices mounted on the vehicle.
Recently, there has been a demand for bidirectional power transmission of EV charger. In addition to charging the on-board battery by electric power supplied from power grid, it would be desirable to transmit electricity from the on-board battery to various electric appliances, such as power grid, home, or on-board battery of another EV. For example, the on-board battery can behave as an emergency power source to supply power from the EV to electric appliances directly.
A bidirectional DC-DC converter is disclosed in Fully Soft-switched Bidirectional Resonant DC-DC Converter with A New CLLC Tank, Wei Chen et al, Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-fifth Annual IEEE, 21-25 Feb. 2010. The bidirectional DC-DC converter has two H-bridge converters whose AC terminals are respectively connected with primary winding and secondary winding of a transformer. Either of the H-bridges is actively controlled and the other is uncontrolled only anti-parallel diodes conducting, such that DC power can be transferred in bidirectional manner. As implemented with MOSFETs, soft-switching technique is achievable when the MOSFETs are employed as the input port inverting device for a forward power transmission, since the switching losses and conduction losses of MOSFETs are lower than IGBTs. However, the body diodes of the MOSFETs are used as the output port rectifier for the backward power transmission, the reverse recovery characteristics of body diode of the MOSFET is usually not good enough due to their relatively slow reverse recovery speed and relatively high reverse recovery current or reverse recovery charge, thus bring about relatively high reverse recovery losses. Besides, slower reverser recovery characteristics of the body diodes may worsen the soft-switching operation condition of the DC-DC converter.